They are great machines and like Bolens, there are alot of attachments for them. I have an early B10 that came with a 9hp engine, a Big Ten that has a 10hp engine and a late B10 with a 10hp engine. Check out www.simpletractors.com to learn more about them. I have about 10 Bolens and about 10 AC/Simplicity tractors. The ACs are more responsive to steering and do a nicer lawn mowing. The Bolens are better pullers and change attachments easier. Both are great tractors. The AC/Simplicities seem to be lower priced. I bought a 10hp Simplicity 3310 with mower, plow, and chains for $200 two years ago. It ran but was filthy. The headlights even work. Have fun with them. Good Luck, Rick

There are many differences between the 9HP and 10hp engines. The 9hp being the Briggs model 23D and the 10hp being the Briggs model 243431. These two engines have different blocks, heads,cranks, rods, pistons, rings, wrist pins, flywheels, coils, carburetors, intake manifolds, among other things. Just keep this in mind if you need to buy any engine parts. Both engines are very durable and have plenty of power. I use my Big Ten often and it's very reliable, but has a 16hp Briggs on it. I have a 243431 10HP engine that I rebuilt for a future Big Ten restoration.